The free form field allows you to put any terms in you want and it will find establishments that have any of the terms specified.
The more you put in, the more you will get.

If you only use the free form search, it will search everything. If you select options below, the free form field is used only for name and description plus what is selected below. The free form field may be empty, only the options selected will be used.

An example of using the free form search with a major section would be searching for a name containing Pizza in the Location Davenport.
This will find all establishments in Davenport that have Pizza in its name. Note that putting pizza, Davenport in the free form search will find all establishments in Davenport and all establishments that are in the category Italian/Pizza, and all establishments with Pizza in its name. A lot more than what you want.

Searches with options selected below create an "AND" search between major sections, such as Location AND Categories. For example,
Location: Davenport plus Categories: Italian/Pizza will find establishments in Davenport that also are in the Italian/Pizza category.
However, selections inside each major section creates an "OR" search, finding establishments with any of the options selected in that major section.
For example, Location: Davenport OR Blue Grass AND Categories: Italian/Pizza OR American AND Features Wi-Fi OR Vegetarian
will search for establishments in Davenport or Blue Grass that are categorized as Italian/Pizza or American and has Wi-Fi or Vegetarian entrees.

The more complex the search, the fewer establishments you will find and has a higher chance of not finding anything.